A touch panel sensor is connected to the display screen of a display device such as a liquid crystal display device or an organic EL device as an input device to be used. Touch panel sensors are used for the operation screens of ATMs of a bank, vending machines, car navigation systems, PDAs (Personal Digital Assistants), and copying machines, and the like because of the ease of use, and, have been widely used for even cellular phones and tablet PCs in recent years. As the detection systems of the input point, mention may be made of a resistance film system, an electrostatic capacitance system, an optical system, an ultrasonic surface elastic wave system, a piezoelectric system, and the like. Out of these, the electrostatic capacitance system is preferably used for a cellular phone or a tablet PC because of the good responsivity, the low cost, the simple structure, and the like.
An electrostatic capacitance system touch panel sensor has, as one example, a structure in which transparent electrodes in two directions are arranged orthogonal to each other on a transparent substrate such as a glass substrate, and the surface is covered with an insulator such as protective glass. When the surface of the touch panel sensor of the configuration described above is touched with a finger, a pen, or the like, the electrostatic capacitance between both transparent electrodes changes. For this reason, by sensing a change in amount of the current flowing via the electrostatic capacitance, it is possible to grasp the touched position.
As the transparent substrate for use in the touch panel sensor of the configuration described above, a substrate only for a touch panel sensor may be used. However, a transparent substrate for use in a display device can also be used. Specifically, for example, mention may be made of a color filter substrate for use in a liquid crystal display device, a glass substrate for use in an organic EL device, or the like. Use of such a transparent substrate for a display device can support the characteristics required of the touch pane sensor such as the improvement of the contrast ratio of a display, the improvement of the brightness, and the reduction of the thickness of a smart phone, or the like.
Recently, in order to improve the tough sensitivity, and to reduce the noise when the transparent electrode is used, use of a low-resistance metal electrode as the electrode has been studied.
However, a metal electrode is high in reflectivity, and is visible to users' naked eyes, namely, is visually recognized, unfavorably resulting in a reduction of the contrast ratio. For this reason, when a metal electrode is used, there is adopted a method in which the metal film is subjected to a blackening treatment to reduce the reflectivity, or other methods.
For example, Patent Literature 1 describes the following method: in order to solve the problem of visibility in a bridge electrode interconnecting conductive transparent pattern cells, a bridge electrode is formed using a black conductive material on an insulation layer formed at the conductive pattern cells. Specifically, there is exemplified a method in which as the bridge electrode, a metal of Al, Au, Ag, Sn, Cr, Ni, Ti, or Mg is blackened into an oxide, a nitride, a fluoride, or the like by the reaction with a chemical. However, Patent Literature 1 only discloses the reflectivity reducing technology of the bridge electrode by the blackening treatment of a metal, and does not pay attention to the reduction of the electrical resistivity at all. Accordingly, the exemplifications include those with a high electrical resistivity such as metal oxides, and cannot be applied to electrodes for low electrical resistivity wiring. Further, the Patent Literature 1 also includes high-reactivity and dangerous substances such as a nitride of Ag and an oxide of Mg, which is poor in utility.